The conventional procedures for cleaning groundwater that has been contaminated with such chlorinated solvents have generally not involved the chemical breakdown of the contaminant, but have merely removed the contaminant from the water. For example, it is known to pass the water over activated carbon, whereby the contaminants are adsorbed onto the carbon. Whilst this is effective to clean the water, the contaminants remain on the carbon: this creates in turn another disposal problem.
Since, as a general rule, the contaminants are volatile, they may also be removed by air-stripping. The water is aerated, which cleans the water, but the problem again remains that the contaminants still exist. It is becoming increasingly unacceptable simply to discharge the contaminated air into the atmosphere, so that the contaminants once again have to be removed, for example by sorbtion onto activated carbon.
An alternative conventional procedure does break down chlorinated contaminants. This procedure involves catalytic oxidation at an elevated temperature; though very expensive, the procedure breaks the contaminants down into carbon dioxide and an appropriate chloride, which is harmless in small concentrations. The procedure is usually out of the question on cost grounds, for a drinking water supply.
In U.S. Pat. No. 4,382,865 (SWEENY, May 10, 1983) there is disclosed a system for treating the effluent created during the manufacture of halogenated pesticides. Here, the effluent water stream, containing the waste material from the pesticide manufactory is passed over a combination of metals, and it is the fact of the combination which is instrumental in causing the breakdown of the halogenated contaminant.
The present invention is concerned, like Sweeny, with removing halogenated contaminants from water; unlike Sweeny, the invention is concerned with removing halogenated contaminants, particularly solvents, from groundwater that is permeating through its native aquifer. It is recognised, in the invention, that a key aspect of such groundwater is that, unlike a factory effluent, groundwater can be expected, as a general rule, to be substantially oxygen-free.
It is recognised, in the invention, that the chemical break-down of halogenated contaminants in in-ground groundwater can be effected much more cheaply than is suggested by the prior art, by using, for example, materials that can be obtained, in the quantities needed, as a discarded by-product from metal-cutting processing.